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Spark Adds To Early But Promising Data For Hemophilia Gene Therapy

The race to develop a gene therapy for hemophilia just moved another few feet forward. Spark Therapeutics, which is one of several companies developing a treatment, is the latest to provide its first glimpse of clinical data in human patients.

As with other snippets from rivals like UniQure, of Amsterdam, and BioMarin Pharmaceutical, of San Rafael, CA, the results—interim data from an early-stage clinical trial—look promising. Investors have bumped Spark (NASDAQ: ONCE) shares up 13 percent as of mid-day. But many questions remain.

No fewer than seven groups are working on a long-lasting treatment for hemophilia using gene therapy. The field has been on a roller-coaster ride for more than two decades, but the lure for drug developers is strong. Hemophiliacs, especially those with a severe form who need frequent infusions of blood-clotting drugs to prevent dangerous bleeding episodes, would benefit from a new standard of care.

That benefit will only arrive if gene therapies safely produce meaningful levels of the clotting factor that patients lack. “Meaningful” doesn’t necessary mean normal. In fact, many in the field believe that simply boosting Factor IX (in severe hemophilia B patients) or Factor VIII (in severe hemophilia A patients) to a fraction of normal levels—5 percent of normal is a threshold commonly cited—would make a big impact. And the higher the number, the better the potential result.

Spark reported today that its hemophilia B treatment, SPK-9001, showed early promise toward that goal. Spark reported on three patients: One had Factor IX levels of 28 percent of normal after 18 weeks, another had 30 percent after seven weeks, and a third had 16 percent at three weeks.

Spark said their levels rose consistently through the first four weeks after treatment, and that while one patient got a precautionary infusion two days after treatment because of a suspected ankle bleed, the other patients haven’t needed additional treatment since the gene therapy has kicked in.

Spark also noted that the patients have not required immunosuppressive steroids to counteract the immune reaction that other gene therapy programs in hemophilia have triggered.

The data come with a number of caveats, starting with the tiny sample size of three patients. The results will have to hold up for a long time, without complications, to be truly meaningful. Such tiny samples would typically not merit as much attention, but in a field of new medical exploration, like gene therapy, every data point is notable, and taken with early but promising data from similar programs, the overall message is “so far, so good.”

The differences between all of these companies are very technical, concerning the viral “vectors” they use to deliver their gene therapies into patients’ cells, or with the genetic material itself. Those differences could eventually result in a range of clinical benefits. Perhaps one therapy eventually will prove safer, or longer-lasting, or beneficial to a certain genetic subtype of patients.